Measuring the dustiness of particulate solids



- INVNTOR ELME'R .A. PIKE' ATTORNEY E. A. PIKEv MEASURING THE DUSTINESS oF PARTICULATE soLIDs Flled oct 29 I 1953 Feb. 1l, 1958 United States Patent C) 2,822,719 y MEAsURlNG THE DUSTINEss oF PARTICULATE soLms Elmer A. Fike, Nitro, ,W. Va., assignor to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware Application ctober 29, 1953, Serial No. 389,017

, 2 Claims. (Cl. 88-14) tants and careful control-of the moisture content.. In

the detergent `field the problem is particularly acute -since the dust of synthetic detergents is irritating to the mucous membranes causing sneezing and discomfort. The dry alkyl benzene sodium sulfonates for example are normally dusting synthetic detergents. Various agents have been discovered which mitigate the dustiness but as is generally the case the solution of the lproblem goes hand in hand with the development of suitable analytical methods. Heretofore a suitable method of evaluating dustiness of particulate solids has not been available.

In accordance with the present invention it has been discovered that a `dust evaluation based upon the measurement of light transmitted through a dust cloud raisedl by the falling particulate solids gives reproducible and significant results. The details of the method will be' clear on reference to the accompanying drawings.

Referring to the drawings, Fig. l is a perspective view of the dust measuring device. Fig. 2 is a cross sectional view from the front of the instrument. Fig. 3 is a cross sectional view from the end of the instrument. Fig. 4 is a detailed plan of the funnel arrangement for introducing the test material. Fig. 5 isa detail of a section of the feed tube illustrating the dismantling.

Referring to Fig. l, the instrument comprises an opaque container or housing which may be constructed of stainless steel, aluminum or wood resting on a wooden base 2. The door 3 serves for removing the sample after the test has been run. On one side in the upper portion of the housing is a support 4 enclosing a photoelectric cell 5. The current from the cell is measured by a microammeter 6. The current, in turn,V depends upon the intensity of light reaching the photoelectric cell from a constant source of light on the opposite side of the test chamber. In other words, the current is a function of the degree to which the dust in the atmosphere of the chamber obstructs the passage of light. The source of light and hence the current is adjusted to a constant value before each test by means of the rheostat 7. The material to be tested is placed in the funnel 9 which is made of either metal or glass from which it falls through the tube S into the test chamber. The feed tube 8 is preferably constructed of aluminum but other metals or glass serve equally well.

Referring to Fig. 2, a sample of the material to be tested is introduced into funnel 9. A 100 gram sample is convenient where the dimensions of the test chamber are width 12 inches, height and depth 7V2 inches. The

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2 plug 14 is connected to the power'source through a voltage regulator not shown. The circuit to the light source 11 is then closed by means of switch 10, the

light beingY focused by lens 12 on the photoelectric cell 5.v

The current of the latter recorded by the microammeter 6 is adjusted to a constant value, say 100 microamperes, by means of the -rheostat. Thereupon thertest material inthe funnel is introduced into the chamber.

Referring to Fig. 4, the material is Vreleased by strik ing the plungerknob 9c which depresses the stopper 9d. Thelatter is held in place by theV spring 9e Workingagainst the brace 9b through which passesthe plunger shaft 9]. Note that the brace is in the upper portion of the funnel so as not to interfere with the ilow of the test sample. A 3%: in. funnel opening and a 2. in. I. D.;

feed tube have been found satisfactory so that upon striking the plunger knob the test material falls rapidly into the tray 15 of the test chambersee Fig. 2. This raises a cloud of dust in the space above the collected solid. A stop watch isstarted when the plunger is depressed and readings taken every 5 seconds on the microammeter` In this connection it is preferable that the falling material does not intercept the beam of light to the photoelectric cell but that the opening 'for the feed tube is located in front of Yit as illustrated or behind so that the obstruction of light is solelyfrom the dust. In

practice it has been found convenient `and desirable to take the lowest reading noted on the microammeter as' the 5 second reading. Readings are'then taken every 5 seconds'for 100 seconds or until substantial equilibrium is reached. v l

Typical data are'set forth below employing as the test material a detergent composition consisting essentially of 40% dodecyl benzene sodium sulfonate and 60% sodium sulfate. The data show duplicate runs on the same test material, illustrating the reproducibility of the data and also comparing the dustiness of an untreated control with the same material treated with approximately 1% on the detergent of a dust abating additive, as for example one of the dust abating products described in my co-pending application Serial No. 289,910, filed May 24, 1952, now Patent No. 2,744,874.

Untreated Treated Seconds Run 1 Run 2 Ave. Run 1 Run 2 Ave.

then provides the total current in microampere seconds;V

Of course it is more convenient simply to jraddr-upall Patented Feb. 11, s,

lower figures.

3 the readings and multiply the total by five. Obviously it is possible to plot the data, plotting current against time in seconds, and obtain the precise value of the area under the -curve by means of `a-planometer. However, this proved to be entirely unnecessary. The results are reproducible Awithinabout 10% making Vthe approximation described. Furthermore, it is not known how much of this variation should be assigned to the method of measurement and how much to the non-homogeneity ofthe samples. -Of course the more dusty the test mate-- rial is lthe lower the current recorded whereas it is preferable to express increased dustiness` by higher, not Therefore, the dustinessis expressed as the difference .in microampere seconds of what -itv would be in the absence of dust. :If the current is adjusted to 1.00 microamperes per second before the test, it is apparent that after 100 seconds the total would be 10,000 microampere seconds in `the `absence of dust. Accordingly, the dust Value in microampere seconds Ais obtained bythe following formula: Dust value: 10,000-5 T where T -s the total of the 'readings taken at the 5 second intervals.

It will be apparent that an accumulative -wattmeter could be used instead of van ammeter and if suiciently sensitive would be preferable as this would avoid the approximation discussed above `and give the total power output directly. However, accumulative wattmeters of the required sensitivity :are noty generallyavailable.

The removal of the'sample in preparation for carrying out other tests is easily accomplished. lReferring -to Fig. 3, the .door 3 is opened andthe tray 15 removed and emptied. A jointed -feed tube as illustrated in Fig. 5

has been .found convenient as this permits dismantling; and storing of the parts in the body of the chamber yfor shipment orrv storage. Two '10 inch sections or an `overall length ofl20 inches for the feed tube is recommended. It is intended to cover all changes and modifications i of the examples ofA the invention herein chosen for purposes of disclosure which do not constitute departures from the spirit and scope of the invention.

What is claimed is:

5 1. A method of evaluating the dustiness of a particulate solid which comprises dropping a given quantity of said particulatey solid from a given height, after the solid has fallen, measuring the extent to which dust in the atmosphere above the solid reduces the light transmission across a section of the space above the solid by determining the light transmission -at frequent intervals until substantial equilibrium is achieved and summing the results. p

2. A `method of evaluating the dustiness of a parlicu late solid which comprises dropping a given quantity of said particulate solid from a given height into a conlined space, after the solid has fallen, measuring the extent to'which edust in the jconned space of the container above the solid reduces the transmission of light across a cross section of said confined space above the solid by recording the minimum 'light transmission after falling, recording the light transmission at frequent intervals thereafter until substantial equilibrium is reached and summing the results.

References Cited-in the le of this patent .UNITED STATES PATENTS 2,042,095 GramA May 26, 1936 2,379,158 Kalischer June 26, 1945 2,597,899 Payne May 27, 1952k OTHER REFERENCES Drinker et al; Photometric methods for studying and estimatingY suspensions of dusts, fumes, and smokes,

The .Journal of Industrial Hygiene, vol. 7, December 1925, pages 567-576. 

1. A METHOD OF EVALUATING THE DUSTINESS OF A PARTICULATE SOLID WHICH COMPRISES DROPPING A GIVEN QUANTITY OF SAID PARTICULATE SOLID FROM A GIVEN HEIGHT, AFTER THE SOLID HAS FALLEN, MEASURING THE EXTENT TO WHICH DUST IN THE ATMOSPHERE ABOVE THE SOLID REDUCE THE LIGHT TRANSMISSION ACROSS A SECTION OF THE SPACE ABOVE THE SOILD BY DETERMNING THE LIGHT TRANSMISSION AT FREQUENT INTERVALS UNTIL SUBSTANTIAL REQUILIBRIUM IS ACHIEVED AND SUMMING THE RESULTS. 